Video-encoding method, video-decoding method, and apparatus implementing same

ABSTRACT

The present invention relates to an inter-layer prediction method and to an apparatus implementing the method. The method may comprise the steps of generating a first block constituted by the value obtained by up-sampling the reconstruction value of a reference block of a reference layer corresponding to the current block; generating a second block constituted by a prediction value derived from intra-prediction mode of the current block; and generating a prediction block of the current block by combining sample values of the first block and the second block. Thus, intra-prediction on the current layer can be performed using the intra-prediction mode information of another layer.

TECHNICAL FIELD

The present invention relates to a video compression technique, and moreparticularly, to a method of parsing compressed video information toprocess a video and an apparatus using the same.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images haveincreased in various fields of applications. As images have higherresolution and higher quality, the amount of information on the imagesalso increases.

With a growing amount of information, multi-functional devices andnetworks with various environments are introduced. Accordingly, the samecontent may be utilized with different levels of quality.

Specifically, as terminals are able to support diverse qualities ofvideos and various network environments are established, a video withgeneral quality is enabled in one environment while a higher-qualityvideo may be available in another environment.

For example, a user may enjoy video content purchased through a portableterminal on a large-screen display with higher resolution at home.

In recent years, as high definition (HD) broadcast services areavailable, a large number of users is getting used to high-resolutionand high-quality videos and service providers and service users also payattention to ultrahigh-definition (UHD) services having a resolutionfour times higher than HDTV.

Thus, there is a need to provide scalability to video quality, forexample, the image quality, resolution, size and frame rate of a video,based on high-efficiency encoding and decoding methods on ahigh-capacity video so as to offer varied qualities of video services indifferent environments for users' demands.

DISCLOSURE Technical Problem

An aspect of the present invention is to provide a method of processinga leading picture having no reference picture and an apparatus using thesame.

Another aspect of the present invention is to provide a method ofpreventing an error in a decoding apparatus and processing a video andan apparatus using the same.

Still another aspect of the present invention is to provide a method ofsupporting random access to a video and decoding a clean random access(CRA) picture and an instantaneous decoding refresh (IDR) picture firstin a bitstream and an apparatus using the same.

Yet another aspect of the present invention is to provide a method ofdealing with an error caused in video processing and an apparatus usingthe same.

Technical Solution

An embodiment of the present invention provides a video processingmethod including receiving a bitstream comprising a plurality ofpictures, and not outputting a leading picture when at least onereference picture for the leading picture that precedes a random accesspoint picture in output order and follows the random access pointpicture in decoding order is unavailable.

The not outputting of the leading picture may include removing anddiscarding the leading picture from the bitstream, and the videoprocessing method may further include decoding pictures after theremoved leading picture.

The leading picture may be excluded from a decoding process and outputprocess.

The pictures after the removed leading picture may be decoded after apredetermined delay time.

The leading picture may include a first leading picture not decodableand a second leading picture decodable, and the removing and discardingof the leading picture from the bitstream may exclude the first leadingpicture from a decoding process and output process.

The leading picture may include a first leading picture not decodableand a second leading picture decodable, and the removing and discardingof the leading picture from the bitstream may remove and discard thefirst leading picture and the second leading picture from the bitstream.

The leading picture may include a first leading picture not decodable,and the removing and discarding of the leading picture from thebitstream may remove and discard the first leading picture from thebitstream.

The leading picture may include a first leading picture not decodableand a second leading picture decodable, and the video processing methodmay further include generating an unavailable reference picture for thefirst leading picture and generating a flag signal blocking output ofthe unavailable reference picture.

The video processing method may further include decoding the secondleading picture.

The leading picture may include a picture absent in the bitstream as areference picture.

The random access point picture may be a clean random access (CRA)picture.

The video processing method may further include receiving flaginformation indicating that the at least one reference picture for theleading picture is unavailable.

The video processing method may further include outputting errorinformation of the bitstream and decoding pictures after the leadingpicture when the at least one reference picture for the leading pictureis determined to be unavailable through the flag information.

The bitstream may be determined not to satisfy predetermined conformancewhen the at least one reference picture for the leading picture isunavailable.

The video processing method may further include outputting errorinformation of the bitstream and decoding pictures after the leadingpicture.

Advantageous Effects

An embodiment of the present invention provides a method of processing aleading picture having no reference picture and an apparatus using thesame.

Another embodiment of the present invention provides a method ofpreventing an error in a decoding apparatus and processing a video andan apparatus using the same.

Still another embodiment of the present invention provides a method ofsupporting random access to a video and decoding a clean random access(CRA) picture and an instantaneous decoding refresh (IDR) picture firstin a bitstream and an apparatus using the same.

Yet another embodiment of the present invention provides a method ofdealing with an error caused in video processing and an apparatus usingthe same.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically illustrating a video encodingapparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram schematically illustrating a video decodingapparatus according to an exemplary embodiment of the present invention.

FIG. 3 illustrates a layered structure of a coded video processed by thedecoding apparatus.

FIG. 4 illustrates a randomly accessible picture.

FIG. 5 illustrates an instantaneous decoding refresh (IDR) picture.

FIG. 6 illustrates a clean random access (CRA) picture.

FIG. 7 illustrates a case where a picture preceding a leading picture isunavailable.

FIG. 8 is a block diagram illustrating a video processing apparatusaccording to an exemplary embodiment of the present invention.

FIG. 9 is a flowchart illustrating a video processing method accordingto an exemplary embodiment of the present invention.

FIG. 10 illustrates removing a leading picture according to an exemplaryembodiment of the present invention.

FIG. 11 illustrates removing a leading picture according to anotherexemplary embodiment of the present invention.

FIG. 12 illustrates removing a leading picture according to stillanother exemplary embodiment of the present invention.

FIG. 13 is a flowchart illustrating a video processing method accordingto another exemplary embodiment of the present invention.

MODE FOR INVENTION

The present invention may be changed and modified variously and beillustrated with reference to different exemplary embodiments, some ofwhich will be described in detail and shown in the drawings. However,these embodiments are not intended for limiting the invention. Theterminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting the technical ideaof the invention. As used herein, the singular forms “a,” “an” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “include” and/or “have,” when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,components, and/or combinations thereof, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or combinations thereof.

Although elements illustrated in the drawings are independently shownfor convenience of description of different distinctive functions in avideo encoding apparatus/decoding apparatus, such a configuration doesnot indicate that each element is constructed by a separate hardwareconstituent or software constituent. That is, at least two elements maybe combined into a single element, or a single element may be dividedinto a plurality of elements to perform functions. It is to be notedthat embodiments in which some elements are integrated into one combinedelement and/or an element is divided into multiple separate elements areincluded in the scope of the present invention without departing fromthe essence of the present invention.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings. Like referencenumerals in the drawings refer to like elements throughout, andredundant descriptions of like elements will be omitted herein.

FIG. 1 is a block diagram schematically illustrating a video encodingapparatus according to an exemplary embodiment of the present invention.Referring to FIG. 1, the video encoding apparatus 100 includes a picturepartitioning module 105, a prediction module 110, a transform module115, a quantization module 120, a rearrangement module 125, an entropyencoding module 130, a dequantization module 135, an inverse transformmodule 140, a filter module 145 and a memory 150.

The picture partitioning module 105 may divide an input picture into atleast one block as a processing unit. Here, the block as the processingunit may be a prediction unit (PU), a transform unit (TU) or a codingunit (CU).

Processing unit blocks divided by the picture partitioning module 105may have a quadtree structure.

The prediction module 110 may include an inter prediction module toperform inter prediction and an intra prediction module to perform intraprediction, which will be described. The prediction module 110 generatesa prediction block by performing prediction on the processing unit ofthe picture from the partitioning module 105. The processing unit of thepicture in the prediction module 110 may be a CU, a TU or a PU.Furthermore, the prediction module 110 may determine whether predictionperformed on the processing unit is inter prediction or intraprediction, and may determine details (for example, a prediction mode)of each prediction method. Here, a processing unit on which predictionis performed may be different from a processing unit for which aprediction method and details on the prediction method are determined.For example, a prediction method and a prediction mode may be determinedfor each PU, while prediction may be performed for each TU.

In inter prediction, a prediction block may be generated by performingprediction based on information on at least one of previous and/orsubsequent pictures of a current picture. In intra prediction, aprediction block may be generated by performing prediction based oninformation on a pixel within the current picture.

A skip mode, a merge mode and motion vector prediction (MVP) may be usedas an inter prediction method. In inter prediction, a reference picturefor a PU may be selected, and a reference block corresponding to the PUmay be selected. The reference block may be selected as a unit of interpixel. Subsequently, a prediction block that has a minimum residualsignal with respect to the current PU and has a minimum-size motionvector is generated.

The prediction block may be generated as an integer sample unit or as apixel unit smaller than an integer pixel, such as a ½ pixel unit and a ¼pixel unit. Here, the motion vector may be represented in a unit smallerthan an integer pixel.

Information including an index of the reference pixel selected in interprediction, the motion vector (e.g., a motion vector predictor) and theresidual signal, is entropy-encoded and transferred to a decodingapparatus. In the skip mode, since the prediction block may be areconstructed block without a residual, the residual may not begenerated, transformed, quantized and transferred.

In intra prediction, a prediction mode is determined by a PU, andprediction may be performed by a PU. Alternatively, a prediction modemay be determined by a PU, and intra prediction may be performed in aTU.

Intra prediction may include 33 directional prediction modes and two ormore non-directional modes. The non-directional modes may include a DCprediction mode and a planar mode.

In intra prediction, the prediction block may be generated afterapplying a filter to a reference sample. Here, whether to apply thefilter to the reference sample may be determined on an intra predictionmode and/or size of a current block.

A PU may have different sizes and forms. For example, in interprediction, a PU may be a 2N×2N, 2N×N, N×2N or N×N block (N is aninteger). In intra prediction, a PU may be a 2N×2N or N×N block (N is aninteger). Here, a PU having an N×N size may be applied only to a specialcase. For example, an N×N PU may be available only for a CU with aminimum size or only for intra prediction. In addition to the PUs withthe foregoing sizes, a PU may include N×mN, mN×N, 2N×mN and mN×2N blocks(m<1).

A residual value (residual block or residual signal) between thegenerated prediction block and an original block is input to thetransform module 115. Also, information on a prediction mode and amotion vector used for prediction are encoded along with the residualvalue by the entropy encoding module 130 and transferred to the decodingapparatus.

The transform module 115 transforms the residual block by a TU andgenerates a transform coefficient.

A transform block is a rectangular block of samples to which the sametransformation is applied. The transform block may be a TU and have aquadtree structure.

The transform module 115 may perform transformation based on aprediction mode applied to the residual block and a size of the block.

For example, when intra prediction is applied to the residual block andthe block has a 4×4 residual array, the transform module 115 maytransform the residual block using discrete cosine transform (DCT).Otherwise, the transform module 115 may transform the residual blockusing discrete sine transform (DST).

The transform module 115 may generate a transform block of transformcoefficients by transformation.

The quantization module 120 may quantize residual values transformed bythe transform module 115, that is, the transform coefficients, togenerate quantized transform coefficients. The coefficients generated bythe quantization module 120 are provided to the dequantization module135 and the rearrangement module 125.

The rearrangement module 125 rearranges the quantized transformcoefficients provided by the quantization module 120. Rearranging thequantized transform coefficients may enhance encoding efficiency in theentropy encoding module 130.

The rearrangement module 125 may rearrange a two-dimensional (2D) blockof the quantized transform coefficients into a one-dimensional (1D)vector using coefficient scanning.

The entropy encoding module 130 may entropy-encode the quantizedtransform coefficients rearranged by the rearrangement module 125.Various encoding methods, such as exponential Golomb, context-adaptivevariable length coding (CAVLC) and context-adaptive binary arithmeticcoding (CABAC), may be used for entropy encoding. The entropy encodingmodule 130 may encode various types of information, such as informationon quantized transform coefficients and block type of a CU, predictionmode information, partition unit information, PU information, transferunit information, motion vector information, reference pictureinformation, block interpolation information and filtering information,received from the rearrangement module 125 and the prediction module110.

Furthermore, the entropy coding module 130 may apply a change to areceived parameter set or syntax as necessary.

The dequantization module 135 dequantizes the values quantized by thequantization module 120, that is, the quantized transform coefficients,and the inverse transform module 140 inverse-transforms the valuesdequantized by the dequantization module 135.

The residual values generated through the dequantization module 135 andthe Client Ref. No.: BPP-2013-0058-US, LG: 13FCVL016US02 inversetransform module 140 are merged with the prediction block predicted bythe prediction module 110, thereby generating a reconstructed block.

FIG. 1 illustrates that a reconstructed block is generated by merging aresidual block with a prediction block through an adder. Here, the addermay be regarded as a separate module for generating a reconstructedblock (reconstructed block generation module).

The filter module 145 may apply a deblocking filter, an adaptive loopfilter (ALF), and a sample adaptive offset (SAO) to a reconstructedpicture.

The deblocking filter may remove block distortion generated onboundaries between blocks in the reconstructed picture. The ALF mayperform filtering based on a value obtained by comparing thereconstructed picture obtained by filtering blocks using the deblockingfilter with the original picture. The ALF may be employed only for highefficiency. The SAO reconstructs an offset difference between theresidual block to which the deblocking filter has been applied and theoriginal picture by a pixel unit, in which a band offset or an edgeoffset is used.

Meanwhile, the filter module 145 may not apply filtering to areconstructed block used in inter prediction.

The memory 150 may store the reconstructed block or picture obtained viathe filter module 145. The reconstructed block or picture stored in thememory 150 may be provided to the prediction module 110 performing interprediction.

FIG. 2 is a block diagram schematically illustrating a video decodingapparatus according to an exemplary embodiment of the present invention.Referring to FIG. 2, the video decoding apparatus 200 may include anentropy decoding module 210, a rearrangement module 215, andequantization module 220, an inverse transform module 225, a predictionmodule 230, a filter module 235, and a memory 240.

When a video bitstream is input from the video encoding apparatus, theinput bitstream may be decoded according to an inverse process by whichthe video encoding apparatus processes video information.

For example, when the video encoding apparatus uses variable-lengthcoding (VLC), such as CAVLC, to perform entropy encoding, the entropydecoding module 210 may perform entropy decoding using the same VLCtable as used in the encoding apparatus. Furthermore, if the videoencoding apparatus uses CABAC to perform entropy ending, the entropydecoding module 210 may also perform entropy decoding using CABAC.

Among pieces of information decoded by the entropy decoding module 210,information for generating a prediction block may be provided to theprediction module 230, and a residual value, that is, a quantizedtransform coefficient, may be input to the rearrangement module 215.

The rearrangement module 215 may rearrange information on the bitstreamentropy-decoded by the entropy decoding module 210, that is, thequantized transform coefficients, based on a rearrangement method usedin the encoding apparatus.

The rearrangement module 215 may reconstruct and rearrange a 1D vectorof coefficients into a 2D block of coefficients. The rearrangementmodule 215 may scan coefficients based on a prediction mode of a currentblock (transform block) and a size of the transform block to generate a2D block of coefficients (quantized transform coefficients).

The dequantization module 220 may perform dequantization based on aquantization parameter provided from the encoding apparatus and therearranged coefficients of the block.

The inverse transform module 225 may perform inverse DCT and/or inverseDST on a result of quantization performed by the video encodingapparatus in response to DCT and DST performed by the transform moduleof the encoding apparatus.

Inverse transformation may be performed on the basis of a transfer unitor a partition unit of a picture determined by the video encodingapparatus. The transform module of the video encoding apparatus mayselectively perform DCT and/or DST depending on a plurality ofinformation elements, such as a prediction method, a size of the currentblock and a prediction direction, and the inverse transform module 225of the video decoding apparatus may perform inverse transformation onthe basis of information on the transformation performed by thetransform module of the video encoding apparatus.

The prediction module 230 may generate a prediction block based oninformation on generation of the prediction block provided from theentropy decoding module 210 and information on a previously decodedblock and/or picture provided by the memory 240.

If a prediction mode for a current PU is an intra prediction mode, intraprediction may be performed based on information on a pixel in a currentpicture to generate the prediction block.

If a prediction mode for the current PU is an inter prediction mode,inter prediction for the current PU may be performed based oninformation on at least one of previous and subsequent pictures of thecurrent picture. Here, motion information necessary for the interprediction for the current PU provided by the video encoding apparatus,for example, information on a motion vector and a reference pictureindex, may be derived by checking a skip flag and a merge flag receivedfrom the encoding apparatus.

A reconstructed block may be generated using the prediction blockgenerated by the prediction module 230 and the residual block providedby the inverse transform module 225. FIG. 2 illustrates that thereconstructed block is generated by the adder merging the predictionblock with the residual block. Here, the adder may be regarded as aseparate module for generating the reconstructed block (reconstructedblock generation module).

When the skip mode is used, the prediction block may be thereconstructed block without transmitting the residual block.

The reconstructed block and/or picture may be provided to the filtermodule 235. The filter module 235 may apply deblocking filtering, SAOand/or AFL to the reconstructed block and/or picture.

The memory 240 may store the reconstructed picture or block to be usedas a reference picture or a reference block and supply the reconstructedpicture to an output unit.

FIG. 3 illustrates a layered structure of a coded video processed by thedecoding apparatus.

The coded video signal may be divided into a video coding layer (VCL)associated with decoding a video and dealing with the video itself and anetwork abstraction layer (NAL) located between the VCL and a lowersystem, which the lower system may transmit and store encodedinformation.

An NAL unit as a basic unit of the NAL serves to map the coded videoonto a bit string of the lower system, such as a file format inaccordance with a predetermined standard, a real-time transport protocol(RTP) and a transport stream (TS).

Meanwhile, a parameter set (picture parameter set, sequence parameterset and video parameter set) corresponding to a header of a sequence anda picture and a supplemental enhancement information (SEI) messageadditionally needed for video decoding are separated from information onthe video (slice data).

As shown in FIG. 3, the NAL unit includes two parts of an NAL header anda raw byte sequence payload (RBSP, resulting data from videocompression) generated in the VCL. The NAL header includes informationon a type of the corresponding NAL unit.

The NAL unit is classified into a VCL NAL unit and a non-VCL NAL unitdepending on the RBSP generated in the VCL. The VCL NAL unit is an NALunit including the information on the video, and the non-VCL NAL unit isan NAL unit including the information (parameter set or SEI message)needed for decoding the video.

The VCL NAL unit may be classified into different types according toproperties and types of a picture included in the NAL unit.

FIG. 4 illustrates a randomly accessible picture.

The randomly accessible picture, that is, an intra random access point(IRAP) picture as a random access point, is a first picture of abitstream in decoding order at random access and includes I slices only.

FIG. 4 shows output order or display order and decoding order ofpictures. As shown in FIG. 4, the output order of the pictures may bedifferent from the decoding order of the pictures. For convenience ofdescription, the pictures are divided into groups.

Pictures in a first group (I) precede the IRAP picture in both outputorder and decoding order, while pictures in a second group (II) precedethe IRAP picture in output order but follow the IRAP picture in decodingorder. Pictures in a third group (III) follow the IRAP picture in bothoutput order and decoding order.

The pictures in the first group (I) may be decoded and output regardlessof the TRAP picture.

The pictures in the second group (II) output before the TRAP picture arereferred to leading pictures, which may cause a problem in a decodingprocess when the TRAP picture is used as a random access point, whichwill be described in detail.

The pictures in the third group (III) following the TRAP picture interms of output and decoding order are referred to as normal pictures.The normal pictures are not used as a reference picture of the leadingpictures.

A random access point in a bitstream at which random access happens isthe TRAP picture, and random access starts as a first picture in thesecond group (II) is output.

Meanwhile, the TRAP picture may be any one of an instantaneous decodingrefresh (IDR) picture and a clean random access (CRA) picture.

FIG. 5 illustrates an IDR picture.

The IDR picture is a random access point when a picture group (GOP) hasa closed structure. The IDR picture is the IRAP picture and thusincludes I slices only. The IRD picture may be a first picture in adecoding procedure or appear in the middle of a bitstream. When the IDRpicture is decoded, all reference pictures stored in a decoded picturebuffer (DPB) are indicated as “unused for reference.”

In FIG. 5, a bar represents a picture, and an arrow indicates referencerelationship as to whether one picture can use another picture as areference picture. An x mark on the arrow indicates that picture(s)cannot refer to a picture indicated by an arrow.

As shown in FIG. 5, a POC of the IDR picture is 32, and pictures havinga POC ranging from 25 to 31 and being output before the IDR picture areleading pictures 510. Pictures having a POC greater than 33 are normalpictures 520.

The leading pictures 510 preceding the IDR picture may use the IDRpicture and other leading pictures as reference pictures but may not usea previous picture 530 preceding the leading pictures 510.

The normal pictures 520 following the IDR picture may be decoded byreferring to the IDR picture, the leading pictures and other normalpictures.

FIG. 6 illustrates a CRA picture.

The CRA picture is a random access point when a picture group (GOP) hasan open structure. The CRA picture is also the IRAP picture and thusincludes I slices only. The IRD picture may be a first picture in abitstream in a decoding procedure or appear in the middle of thebitstream for normal play.

The CRA picture may be present in the middle of the bitstream as arandom access point when coded pictures are spliced or the bitstream iscut in the middle.

In FIG. 6, a bar represents a picture, and an arrow indicates referencerelationship as to whether one picture can use another picture as areference picture. An x mark on the arrow indicates that picture(s)cannot refer to a picture indicated by an arrow.

Leading pictures 610 preceding the CRA picture may use all of the CRApicture, other leading pictures and a previous picture 630 preceding theleading pictures 710 as reference pictures.

However, normal pictures 620 following the CRA picture may be decoded byreferring to the CRA picture and other normal pictures but may not usethe leading pictures 610 as reference pictures.

FIG. 7 illustrates a case where a picture preceding a leading picture isunavailable.

Leading pictures 710 precede a CRA picture in output order, and thus areoutput before the CRA picture but decoded after the CRA picture. Theleading pictures 710 may refer to at least one of previous pictures 730.

As shown in FIG. 7, when a bitstream is cut in the middle or missed, orrandom access unexpectedly happens to the CRA picture as a picture isspliced, the previous pictures 730 preceding the CRA picture in decodingorder may be unavailable. As the previous pictures 730 as possiblereference pictures of the leading picture 710 are unavailable, a leadingpicture referring to an unavailable picture may not be properly decoded.

A case where a reference picture of a leading picture is unavailable mayinclude cases where a leading picture includes a picture absent in abitstream as a reference picture or a reference picture of a leadingpicture is not present in a decoded picture buffer (DPB).

To solve the foregoing problem, a video processing apparatus accordingto an exemplary embodiment of the present invention does not output aleading picture that refers to an unavailable reference picture.

FIG. 8 is a block diagram illustrating a video processing apparatusaccording to an exemplary embodiment of the present invention. As shownin FIG. 8, the video processing apparatus 800 includes a bitstreamreceiver 810 and a video processor 820.

The video processing apparatus 800 may include a module or deviceincluding the video processor 820 to perform a decoding process. Thevideo processing apparatus 800 may be provided as a television, a videoplayer and various terminal capable of decoding and outputting a video.

The bitstream receiver 810 receives a bitstream including a plurality ofpictures.

The bitstream received by the bitstream receiver 810 is output as avideo via a decoding process by the video processor 820.

The bitstream receiver 810 may include a parsing module to parse theinput bitstream to obtain information needed for decoding the pictures.

The video processor 820 may include a decoding apparatus including thecomponents described in FIG. 2 or a decoding module to perform decoding.The vide processor 820 of the present embodiment determines whether tooutput a leading picture based on availability of a reference picture.

FIG. 9 is a flowchart illustrating a video processing method of thevideo processing apparatus 800 according to an exemplary embodiment ofthe present invention.

The video processing apparatus 800 receives a bitstream including aplurality of pictures (S901).

The pictures may include an IDR picture or CRA picture as a randomaccess point. Further, the pictures may include a leading picture thatprecede a random access point picture in output order but follow therandom access point picture in decoding order.

The video processor 820 does not output the leading picture when atleast one reference picture of the leading picture is unavailable(S902).

Operation of not outputting the leading picture may include removing anddiscarding the leading picture from the bitstream. The discarded leadingpicture is excluded from a decoding process and an output process.

When a leading picture referring to an unavailable reference picture ispresent, the video processor 820 determines that the bitstream satisfiespredetermined bitstream conformance and performs a default behavior ofexcluding the leading picture from an output video.

The default behavior is performed though a leading picture is notdecodable, thereby preventing malfunction and errors that may occur inthe video processing apparatus 800. Moreover, the video processingapparatus 800 may properly process a bitstream in which unexpectedrandom access happens.

After the leading picture is excluded from the decoding process and theoutput process, the video processor 820 decodes pictures following theexcluded leading picture (S903).

The pictures following the excluded leading picture refer to picturesnormally decodable regardless of a missed reference picture or an absentreference picture in the bitstream.

Here, the video processor 820 delays decoding a subsequent picture for apredetermine delay time so as to maintain a picture bit string of theinput bitstream, that is, to prevent overflow or underflow of a bufferstoring the pictures. The video processor 820 may include a codedpicture buffer (CPB) to store a coded picture and a decoded picturebuffer (DPB) to store a decoded picture.

FIG. 10 illustrates removing a leading picture according to an exemplaryembodiment of the present invention.

As shown in FIG. 10, a leading picture may include a first leadingpicture 1010 and a second leading picture 1020.

The pictures included in the first group I may include a picture thatthe leading pictures cannot refer to. The first group I may includepictures to be currently decoded, that is, a CRA picture and picturesirrelevant to the leading pictures 1010 and 1020.

The first leading picture 1010 refers to a picture that is not normallydecoded, for example, a picture referring to an unavailable referencepicture, and the second leading picture 1020 is a picture to be normallydecoded regardless of the first leading picture 1010.

Among the leading pictures 1010 and 1020, B0, B1 and B2 are firstleading pictures 1010, and B3 to B6 are second leading pictures 1020.

According to the present embodiment, the first leading pictures 1010which are not decodable are excluded from the decoding process and theoutput process. The first leading pictures 1010 may be removed anddiscarded from the bitstream.

The video processor 820 decodes and outputs the second leading pictures1020, excluding the first leading pictures 1010 from the decodingprocess and the output process. As the second leading pictures 1020 areoutput, random access starts.

Here, the video processor 820 may delay decoding the second leadingpictures 1020 in view of bitstream timing with respect to the removedleading pictures 1010.

FIG. 11 illustrates removing a leading picture according to anotherexemplary embodiment of the present invention.

As shown in FIG. 11, a leading picture may include a first leadingpicture 1110 and a second leading picture 1120.

As mentioned above, the first leading picture 1110 refers to a picturethat is not normally decoded, for example, a picture referring to anunavailable reference picture, and the second leading picture 1120 is apicture to be normally decoded regardless of the first leading picture1110.

Among the leading pictures 1110 and 1120, B0, B1 and B2 are firstleading pictures 1110, and B3 to B6 are second leading pictures 1120.

According to the present embodiment, the video processor 820 may excludenot only the first leading pictures 1110 which are not decodable butalso the second leading pictures 1120 normally decodable from thedecoding process and the output process. The video processor 820 mayremove and discard the first leading pictures 1110 and the secondleading pictures 1120 from the bitstream.

The video processor 820 decodes and outputs pictures after the firstleading pictures 1110 and the second leading pictures 1120 which areexcluded from the decoding process and the output process, that is, thepictures in the third group III.

Here, the video processor 820 may delay decoding a subsequent picturefor a predetermine delay time so as to prevent overflow or underflow ofa buffer of the removed leading pictures 1110 and 1120.

After the predetermined delay time since the CRA picture as a randomaccess point is decoded, the pictures in the third group III are decodedand the decoded CRA picture and pictures in the third group III aresequentially displayed.

FIG. 12 illustrates removing a leading picture according to stillanother exemplary embodiment of the present invention.

As shown in FIG. 12, a leading picture may include a first leadingpicture 1210 that refers to an unavailable reference picture only. Thatis, pictures B0 to B6 in the second group II after the CRA picture arefirst leading pictures 1210 that refer to an unavailable referencepicture.

The video processor 820 may exclude all first leading pictures 1210 notdecodable from the decoding process and the output process. The firstleading pictures 1210 may be removed and discarded from the bitstream.

The video processor 820 decodes and outputs the pictures in the thirdgroup III after the first leading pictures 1210 excluded from thedecoding process and the output process.

After a predetermined delay time since the CRA picture as a randomaccess point is decoded, the video processor 820 decodes the pictures inthe third group III and sequentially outputs the decoded CRA picture andthe pictures in the third group.

FIG. 13 is a flowchart illustrating a video processing method accordingto another exemplary embodiment of the present invention.

A bitstream including a plurality of pictures is received (S1301).

Pictures may include a random access point picture, a leading picturethat precedes the random access point picture in output order andfollows the random access point picture in decoding order, and a normalpicture that follows the random access point picture in both outputorder and decoding order. The leading picture may include at least oneof a first leading picture not decodable and a second leading picturedecodable. The first leading picture may refer to a picture absent inthe bitstream or an unavailable picture.

When the first leading picture is present in the bitstream, the videoprocessor generates an unavailable reference picture for the firstleading picture (S1302).

Although the first leading picture is not output and does not affect adecoding process of another picture, the video processor operates as ifthe first leading picture is decoded, by generating the unavailablereference picture for the first leading picture, that is, a virtualreference picture.

A sample value of the unavailable reference picture may be generated asan median value of a possible sample value that the picture has.

The video processor sets a flag signal indicating whether to output ofthe unavailable reference picture to 0 so as not to output the pictureand processes the first leading picture not to be output (S1303).

After processing the first leading picture not decodable, the videoprocessor decodes the second leading picture normally decodable.

According to the present embodiment, the video processing apparatus mayreceive flag information on the leading picture and process the leadingpicture based on the received flag information. Table 1 illustrates asyntax including the flag information on the leading picture.

TABLE 1   Descriptor seq_parameter_set_rbsp( ) {  ... broken_link_leading_pics_enable_flag u(1)  ... }

In Table 1, when broken_link_leading_pics_enable_flag is 1, at least onereference picture for the leading picture is unavailable. Whenbroken_link_leading_pics_enable_flag is 0, the leading picture does notinclude the unavailable reference picture. For instance, when thereference picture is missed, broken_link_leading_pics_enable_flag is 1.

When broken_link_leading_pics_enable_flag is 1, the video processor mayremove the leading picture including the unavailable reference picturefrom the decoding process and the output process.

The leading picture may include the first leading picture not normallydecodable and the second leading picture normally decodable.

The video processor may remove only the first leading picture from thedecoding and output processes or remove all leading pictures from thedecoding and output processes regardless of the first and second leadingpictures.

Alternatively, the video processor may generate an unavailable referencepicture for the first leading picture including the unavailablereference picture. In this case, the generated unavailable referencepicture and the first leading picture are not output.

To sum up, the video processor may receive flag information indicatingthat at least one reference picture for the leading picture isunavailable and perform one of operations illustrated in FIGS. 10 to 13based on the flag information.

Meanwhile, the video processing apparatus may not only receive flaginformation broken_link_leading_pics_enable_flag but also analyzeproperties of the pictures included in the bitstream to setbroken_link_leading_pics_enable_flag.

The video processor may remove the leading picture from the decoding andoutput processes based on the flag information set up in an upper systemlevel.

according to another exemplary of the present embodiment, when the flaginformation of Table 1 is received, the video processor may determinethat the bitstream does not satisfy the predetermined bitstreamconformance and perform a corresponding subsequent operation.

For example, the video processor may stop decoding a video and output anerror caused in the decoding process. Error information may be reportedto an upper system level of the video processor, for example, anapplication or video player level. The video processor may receive aninstruction on a subsequent operation against the error from the uppersystem level or perform a default operation.

The video processor may output the error and then decode decodablepictures after the leading picture.

Alternatively, the video processor may determine that the bitstream doesnot satisfy the predetermined bitstream conformance when at least onereference picture for the leading picture is unavailable.

That is, when a picture not normally decodable is found, the videoprocessor may determine that the bitstream does not satisfy thepredetermined bitstream conformance and perform a correspondingsubsequent operation even though the flag information on the leadingpicture is not received.

The video processor may stop the decoding process and output the errorcaused in the decoding process. Error information may be reported to anupper system level of the video processor, for example, an applicationor video player level. The video processor may receive an instruction ona subsequent operation against the error from the upper system level orperform a default operation.

The video processor may output the error and then decode decodablepictures after the leading picture.

Although methods of illustrative systems have been described with aseries of stages or blocks based on the flowcharts, the presentinvention is not limited to the foregoing sequence of the stages. Somestages may be carried out in different order from described above or atthe same time. Further, it should be noted that as the aforementionedembodiments may include various aspects of examples, combinations of theembodiments may be also understood as exemplary embodiments of thepresent invention. Thus, it will be appreciated by those skilled in theart that changes, modifications and alternatives may be made in theseexemplary embodiments without departing from the principles and spiritof be the invention, the scope of which is defined in the appendedclaims and their equivalents.

1-15. (canceled)
 16. A video decoding method comprising: receiving abitstream comprising an instantaneous decoding refresh (IDR) picture ora clean random access (CRA) picture; decoding the IDR picture or the CRApicture; and decoding a picture that precedes the IDR picture in outputorder and follows the IDR picture in decoding order by referring to atleast one of the IDR picture and a picture that is decoded after the IDRpicture and decoding a leading picture that precedes the CRA picture inoutput order and follows the CRA picture in decoding order by referringto at least one of the CRA picture, a picture that is decoded before theCRA picture and a picture that is decoded after the CRA picture, whereinthe leading picture is not output when a random access happens to theCRA picture and at least one reference picture for the leading pictureis unavailable.
 17. The video decoding method of claim 16, wherein theleading picture is discarded from the bitstream, and the video decodingmethod further comprises decoding pictures after the leading picturewhen the leading picture is discarded
 18. The video decoding method ofclaim 16, wherein the leading picture is neither decoded nor output. 19.The video decoding method of claim 18, wherein the pictures after theleading picture that is neither decoded nor output are decoded after apredetermined delay time.
 20. The video decoding method of claim 16,wherein the leading picture comprises a first leading picture notdecodable and a second leading picture decodable, and the first leadingpicture is neither decoded nor output.
 21. The video decoding method ofclaim 16, wherein the leading picture comprises a first leading picturenot decodable and a second leading picture decodable, and the firstleading picture and the second leading picture are neither decoded noroutput.
 22. The video decoding method of claim 16, wherein the leadingpicture comprises a first leading picture not decodable, wherein thefirst leading picture is neither decoded nor output.
 23. The videodecoding method of claim 16, wherein the leading picture comprises afirst leading picture not decodable and a second leading picturedecodable, and the video decoding method further comprises generating anunavailable reference picture for the first leading picture andgenerating a flag signal preventing output of the unavailable referencepicture.
 24. The video decoding method of claim 23, further comprisingdecoding the second leading picture.
 25. The video decoding method ofclaim 16, wherein the leading picture contains a reference picture thatis not present in the bitstream.
 26. The video decoding method of claim16, further comprising receiving flag information indicating that the atleast one reference picture for the leading picture is unavailable. 27.The video decoding method of claim 26, further comprising outputtingerror information of the bitstream and decoding pictures after theleading picture when the at least one reference picture for the leadingpicture is determined to be unavailable through the flag information.28. The video decoding method of claim 16, wherein the bitstream isdetermined not to satisfy predetermined conformance when the at leastone reference picture for the leading picture is unavailable.
 29. Thevideo decoding method of claim 28, further comprising outputting errorinformation of the bitstream and decoding pictures after the leadingpicture.